Changes in the fish communities of the Breede and Mbashe estuaries were investigated in relation to the environmental variables that influence the fish assemblages in these systems. The Breede Estuary (34° 24’21.6”S, 20° 51’ 08.2”E) occurs within the warm-temperate/cool-temperate transition-zone, while the Mbashe Estuary (32o 14' 55.4"S, 28o 54' 03.7"E) falls within the subtropical/warm-temperate transition-zone along the South African coastline. The Breede Estuary was sampled (seine and gill nets) during summer (January-March) over a period of 10 years (2002-2012), while the Mbashe Estuary was sampled (seine net) during spring (October) over a period of three years (2010-2012). The proportion of tropical fish species was higher in the Mbashe Estuary compared to the Breede Estuary, while the Breede Estuary contained a higher proportion of temperate species than the Mbashe Estuary. Although the abundance of individual species in both estuaries varied, the ranking of species in the Breede Estuary was stable over the 10 year period. Multivariate analysis showed that the fish communities within each reach (upper, middle, lower) of the Breede Estuary remained similar, regardless of year. In contrast, species composition in the Mbashe Estuary differed significantly between years mainly due to differences in the river flow regime during the study period. Environmental variables responsible for structuring the fish assemblage in each estuary differed. Salinity significantly impacted the spatial fish assemblage structure of the Breede Estuary, with most of the species recorded being associated with the more saline lower reaches. The abundance of tropical species near their distributional limit in the Breede Estuary appeared to be impacted by sea surface temperature (SST) as peak total abundance of these species coincided with the warmest SST, while the lowest total abundance coincided with the coldest annual SST during the study period. The fish assemblage structure in the Mbashe Estuary was impacted by differing freshwater input prior to sampling, with flooding negatively impacting the mean total abundance, species composition and diversity in this system. The variables that influenced the fish assemblage structure of both transition-zone estuaries will be affected by climate change in the future. These variables will, in turn, determine the composition, abundance and diversity of species within these important estuarine systems. In order to measure these impacts with any degree of understanding, long-term studies on the abiotic and biotic (including the ichthyofauna) features of these estuaries are required to interpret climate change trends.

Models of phenology of the pine false webworm (PFW), Acantholyda erythrocephala and one of its parasitoids were developed from relationships between PFW spatial distribution and microweather. Development of subterranean stages of PFW was simulated from rate-summation models developed from nonlinear regression equations describing the relationship between temperature and rate of development of post-diapause prepupae and pupae. Defoliation caused by PFW increased the soil's exposure to solar radiation resulting in higher soil temperatures and a corresponding reduction in development time of subterranean stages. Predictability was enhanced slightly when the distribution of insects and temperature of the soil were incorporated into the model. Increasing the time increment used in the model from 1 to 4 h did not adversely affect its resolution. Mating and oviposition of PFW occur within a few hours of emerging from the soil and the majority of PFW eggs were mature and ready for deposition at female emergence. Potential fecundity of PFW was accurately predicted from adult wet and dry weights. The oviposition pattern of PFW was also described by a model based on temperature-dependent oviposition and ageing rate functions. The effect of larval web construction on the development of arboreal stages was investigated. When exposed to sunlight, the web traps heat and raises the body temperature of its inhabitants. A model was developed and used to examine the significance of the web microclimate for development of larvae. Relationships between web temperatures, canopy temperatures and standard meteorological methods were developed to permit using data from standard weather stations to drive the model. Larval development increased by 1.4 to 2.8 d when estimated web temperatures were incorporated into the model, while development was retarded by 2.6 to 4.0 d when canopy temperatures were used instead of meteorological screen temperatures. Two ichneumonid parasitoids, Sinophorus megalodontis and an undescribed species of Olesicampe were reared from eonymphs of PFW. Morphological methods for distinguishing the immature stages of the parasitoids were developed. A predictive model for subterranean development and adult longevity of Olesicampe sp. was used to describe and to compare phenological observations from emergence traps, Malaise traps and dissections of host larvae. The effectiveness of the parasitoids as natural control agents is discussed in relation to host synchrony, encapsulation, and multi- and superparasitism. / Land and Food Systems, Faculty of / Graduate

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Tropical forests represent major uncertainties in climate models and have the potential to act as both net carbon sources and sinks in the future. Projections that hurricanes will be an increasingly powerful disturbance in many tropical forests further complicate our ability to predict how these ecosystems will respond to climate change. By understanding how environmental variation at small spatial scales affects ecosystem processes shaping present-day forests, it may be possible to improve our predictions for how these forests will change in the future. This dissertation consists of three chapters examining the spatial patterns of tree species and soil greenhouse gas fluxes in a tropical forest in the Luquillo Experimental Forest, Puerto Rico. Disentangling the forces that drive the spatial distribution of tree species has been a foundational question in ecology and determining the relative importance of these forces is central to understanding spatial variation in soil biogeochemistry. In chapter 1, I use percolation threshold analysis to examine the clustering patterns of simulated and real tree spatial point patterns to understand the role that environmental filtering and density dependent processes play in shaping tree species distributions. I demonstrate that percolation threshold analysis successfully distinguishes thinning by random, environmental filtering, and density dependent processes. Additionally, the relative importance of these thinning processes varies by species’ traits; fast growing species with low LMA and shade intolerance have stronger evidence of density dependent processes compared to species with high LMA and shade tolerance. In chapter 2, I examine the spatial relationships between soil greenhouse gas fluxes and two proximal drivers of soil environmental variation: tree species and topography. I also examine how incorporating small-scale variation in greenhouse fluxes affects our scaled-up estimates of ecosystem greenhouse gas emissions. I show that including species effects improves estimates of soil CO2 fluxes, and including measures of topography improve estimates of CH4 and N2O fluxes. Incorporating spatial variation in GHG fluxes related to tree species and topography into our estimates of ecosystem GHG emissions decreased estimates of the total CO2-equivalent emissions in this forest by 5%. Finally, in chapter 3 I examine how the GHG fluxes in this forest change after an intense hurricane. I demonstrate that GHG emissions shift following a hurricane; this shift is primarily driven by a 176% increase in N2O emissions that represent a significant net loss of gaseous nitrogen from this forest. N2O fluxes accounted for 4.2% of the post-hurricane GHG-induced radiative forcing (compared to 1.8% pre-hurricane) and the combined increase in CO2, CH4, and N2O emissions observed translates to a 25% increase in CO2-equivalent emissions compared to pre-hurricane conditions. This dissertation focuses on the role of small-scale environmental variation in shaping forest communities and spatial patterns of GHG fluxes and aims to highlight how this variation can help us to better understand the role tropical forests play in the biosphere.

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The cooling preceding the beginning of North American continental glaciation is beautifully represented by the thick fluvial and lacustrine sequences of the Pliocene Glenns Ferry Formation at the Hagerman Fossil Beds National Monument (HAFO), Idaho. This time interval is commonly studied because it contains the elevated global temperatures predicted to result from continued anthropogenic warming. The fossil mammals at HAFO were examined to see the effects of climate change on past mammalian assemblages. The nature of the fossiliferous localities at HAFO was documented to establish which localities could be considered in situ. Additionally, the structural architecture of the beds was mapped to establish an idealized stratigraphic datum to which localities were tied. This facilitated temporal comparison of the widespread localities at HAFO. Second, a high-resolution record of climate change was created using global climate models to predict which oceanic areas varied in temperature in concert with HAFO during the middle Pliocene. Data from deep-sea cores from those oceanic areas were combined to create a proxy temperature pattern; such a detailed record from terrestrial data in the Glenns Ferry Formation is not currently possible. Selected mammalian groups, carnivorans, insectivorans, and leporids, were examined in light of the established climatic patterns. The cooling through the lower portion of the Glenns Ferry Formation corresponds to variation in the morphology of individual species, the relative abundance of species, and the species-level diversity of mammalian groups. There is a return to warm temperatures near the top of the section at HAFO, and the mammals returned to the conditions exhibited before the cool-temperature extreme. This faunal resilience, however, occurred over hundreds of thousands of years. The final paleoecologic approach established correlations between the species diversity of groups of modern mammals and modern climatic values. Many modern groups were found to be highly-significantly correlated to climate, but when the established predictive equations were applied to HAFO, the results were variable. Estimates of annual precipitation varied widely, depending on the taxonomic group, and also deviated from precipitation estimates from sedimentology. Temperature patterns were more consistent with each other and with the pattern of the deep-sea core proxy. / text